Color photographic process



COLOR PHOTOGRAPHIC PROCESS Filed Aug. 27, 1945 (Lighl' Sensilive FerricSalls .Prinled by Exposure Through Appropriale Color Record and WashedIn Wal'er +0 Form Prussian Blue Image Prussian Blu-e g?) and RemoveUnexposed Ferric Salls Dye Base,Mordanled lo Prussian Blue lmage.Reacledwilh Coupler +0 Form Dye Image and Prussian Dye Image Blue RemovedResensi'lizing wilh Ferric S alls and Repealing Above Sleps 2SLigh'l-Sensilive Carrier Supporl 22 L 2 Lighl-Sensillve Carrier FIG. 2

lNVENTOR Patented July 6, 1948 NITED STATES OFFICE COLOR PHOTOGRAPHICPROCESS Helen P. Husek, Allston, Mass, assignor to Polaroid Corporation,Cambridge, Mass, a corporation of Delaware Claims.

This invention relates to photographic processes and more particularlyto methods for forming black and white and single color and multicolorreproductions in two or three dimensions in carriers sensitized withferric salts.

Objects of the invention reside in the provision of methods for formingimages, designs, indicia and the like in black and white and in colorsby dye toning images of Prussian blue (water-insoluble ferricferrocyanide) derived from lightsensitive ferric salts andpreferentially formed in any hydrophilic material, for exampleorientable plastics such as polyvinyl alcohol, as well as insubstantially unorientable materials such as gelatin and the like, whichlatter materials may be considered as transparent, hydrophilic plasticsand also in other substantially unorientable materials such as paper,textiles and the like; to provide methods of the character describedwherein dye images are formed by mordanting a dye base to the Prussianblue salt and coupling the dye base to form a soluble dye or aninsoluble dye; and to provide techniques for the formation of dye imageswhereby the images remain substantially fixed in or substantive to thecarrier material in which they are formed.

Other objects of the invention are to provide methods for the formationof multicolor images in hydrophilic carrier layers which are ofmaterials of the character described and which are renderedlight-sensitive with ferric salts and also to provide methods whereby ahydrophilic carrier layer, which may or may not be transparent and whichis initially rendered light-sensitive with ferric salts, is successivelyexposed through the individual color records of one or more multicolorimages and is successively treated by dye toning practices to provideindividual components of one or more multicolor images therein, thecarrier layer being re-sensitized with ferric salts prior to color imagecomponent formation which succeeds formation of the first color imagecomponent and any mordant or Prussian blue image formed in carrying outthe process being removed after the formation of its associated dyeimage.

Further objects of the invention comprehend the provision of dye toningmethods of the character described wherein dyes, used to form colorimages, are placed in selected portions or areas of material of thekinds noted to form black and white, or single color or multicolorimages in two dimensions or, when dichroic dyes are used in molecularlyoriented, transparent, hydrophilic, linear polymeric plastics for imageformation, to

, Z form light-polarizing, two dimensional, black and white or singlecolor or multicolor images or to provide pairs of such light-polarizingimages in black and white or in color which if formed as left-eye andright-eye images will give three dimensional or stereoscopicreproduction.

The invention accordingly comprises the several steps and the relationand order of one or more of such steps with respect to each of theothers, which are exemplified in the following detailed disclosure, andthe scope of the application of which will be indicated in the claims.

The above and other objects and novel features of this invention willmore fully appear from the following detailed description when the sameis read in connection with the accompanying drawings. It is to beexpressly understood, however, that the drawings are for purposes ofillustration only and are not intended as a definition of the limits ofthe invention, reference being primarily had for this latter purpose tothe appended claims.

For a fuller understanding of the invention, ref erence should be had tothe accompanying drawing, in which:

Figure 1 is a diagrammatic illustration of one embodiment of film usablewith the invention and shows the manner of processing the same formulticolor image formation therein; and

Fig. 2 is a diagrammatic representation of another embodiment of filmusable for carrying out the invention.

As indicated in the objects, the invention intends to employ anytransparent or opaque material as a photosensitive carrier which is of ahydrophilic nature whereby light-sensitiveferric salts may be introducedtherein by imbibitionor casting. Suitable materials for this purposecomprise orientable plastics, for example polyvinyl alcohol; materialssuch as gelatin, fish glue, albumen and starch which have not beenobtained in an oriented condition suitable for the formation oflight-polarizing images; paper;and textiles such as cotton, silk andWool as well as other fibers, both natural and synthetic which may [bewoven or knitted.

' Dye image formation in any carrier which is sensitized with ferricsalts is eifected by preferentially exposing the carrier, developing thecarrier to form a mordant or metallic salt image of Prussian blue in theexposed portion thereof, and mordanting a dye base to the Prussian blueimage and subsequently converting the dye base to a dye by reacting thedye base with a coupler, re-

3 moval of the mordant or metallic salt being carried out to completethe processing.

A plurality of color images, each of which represents a component of amulti-color image, may be successively formed in a single carrier layerby successively exposing the layer through suitable color records and byrepeating the procedure noted above,it being necessary in this practiceto re-sensitize the layer with ferric salts following the formation ofeach color-image component except the last image component to beproduced.

In the numerous carrier materials heretofore mentioned it will beappreciated that. a number of these materials are admirably suited foruse in photographic films and papers. While it is to be understood thatthe invention has wide application, an explanation thereof may be easilytmderstood by considering the formation and processing of photographicfilms with which the inventionmay be practiced.

.Qne form of film for use with the invention is schematically shown inexaggerated scale in the flow. diagram of Fig. 1 as comprising a base orsupport formed of a transparent plastic upon which is mounted a carrierlayer ll formed of a transparent, hydrophilic material which is adaptedto be. rendered light-sensitive and which may or may not be molecularlyoriented. A film of this character may have a single dye image formed inthe carrier layer or the carrier may have several images, each of whichrepresents a component of a multicolor image, formed therein. When thecarrier H is formed of molecularly oriented plastic, light-polarizingimages may be formed therein.

Another form of film may comprise a support upon which several.image-carrying layers are mounted. For example, two carrier layers maybe, superposed on the same. side of the support or, a single carrierlayer may be mounted on each of the opposite sides of the support. Afilm of the. latter type is shown schematically and in enlarged scale inFig. 2 wherein a carrier layer 2! is disclosed as mounted upon one sideof a base or support 20 and the carrier layer 22 is mounted upon theother side of the support.

The film of Fig. 2' is. suited for a variety of uses. For example. itmay be employed in two dimensional multicolor reproduction by formingone or more color image components in one of the carrier layers thereofand at least one color image component in the other carrier layer. Inboth instances, the'color images could'be made of a light' polarizingor' non-polarizing character depending on the use of molecularlyoriented or unoriented carrier material andby employing dichroicornon-dichroic dyes. When polarizing two-dimensional images are formed,the oriented image-carrying layers are positioned so that the directionof orientation of the molecules of each layer are parallel.

If thecarriers 2!. and 22-are formed of molecularly.v orientedmaterialsandare positioned so that the directionof orientation of the. moleculesof one, layer, is at 90 with respect to that of the other layer, thefilm of Fig. 2 is especially suited for stereoscopic reproduction. Onelayer has one or more light-polarizing left-eye images ofastereoscopicpair formed therein while the other carrier layer has oneor more light-polarizing right-eye images formed therein. Stereoscopicimage pairs in black and white or in a single color" or inmulticolor maybe formed in the carriers-2l and 22.

Molecularly oriented plastics when used as carriers may be renderedlight-polarizing by dyeing the image portions thereof with a dye whichpossesses substantial dichroism. However, if orientable materials areused in a substantially unoriented condition, a dichroic dye whiledyeing them will not render them light-polarizing. Many dyes aredichroic to some extent. Numerous dyes, however, do not possesssufiicient dichroism to provide usable light-polarizing images whenincorporated in molecularl oriented plastic for the purpose of providingstereoscopic reproductions and are referred to in the specification andclaims as being substantially nondichroic along with dyes which show nodichroism.

Prussian blue is an excellent mordant for a dye base which can beconverted to a dye. Thus a Prussian blue image formed in a carrier bypractices to be hereinafter described may be used as a inordant topermit a dye to be selectively placed in the carrier. In accordance withthe invention the dye will occupy an area or portion of the carrierwhich is substantially congruent to and which overlies that portion ofthe carrier occupied by the Prussian blue image and will have an opticaldensity which corresponds to that of the Prussian blue image. If thecarrier is molecularly oriented and the dye employed is a dichroic dye,the Prussian blue image is reproduced as a dichroic or light-polarizingimage having portions therein of differing optical densities or degreesof contrast which are a function of the direction of vibration of theincident light,

From the foregoing it will be appreciated that the invention isadmirably adapted for black and white or single color or multicolorreproduction by providing either polarizing or nonpolarizing images. Bythe use of a film such as that schematically illustrated in Fig. 1comprising a support l9 and a carrier H, it is possible to form a singledye image in a single sensitized plastic carrier or aplurality of dyeimages, each of a color appropriate for a color component of a scene orview to be reproduced, may be successively formed in said singlecarrier. Also, as heretofore intimated in connection with the film ofFig. 2 having the carriers 2! and 22, stereoscopic reproduction in colormay be obtained by the-use of two sensitized and molecularly orientedcarriers arranged so that the orientation axis of the molecules of onecarrier is at 9th to the orientation axis of the other carrier.

In all modifications-of the invention wherein light-polarizing imagesare to be produced, each plastic carrier layer for a color image is asheet of a transparent, hydrophilic, high molecular weight, linearpolymer. A suitable polymer should be able to form a dichroic sorptioncomplex with certain organic dyes and should be orientable and thereforeshould possess a relativelyhigh tensile strength. Polymers characterizedby having a multiplicity of hydroxy groups extending off the mainpolymer chain and consisting of simple repetitive groupings or units aregenerally useful as carriers and examples thereof comprise polyvinylalcohol, polyhydroxy alkane, partially hydrolyzed polyvinyl acetals andpolyvinyl alcohol esters, amylose and regenerated cellulose. In additionother plastics such as suitably prepared polyamides or nylon typeplastics may be employed for carrier materials. Of the plastics hereinnamed, polyvinyl alcohol is preferred.

To make long chain plastics of this character light-polarizing, theirmolecules must be" substantially oriented and the plastics must be dyed5. or stained with a dichroic material. Orientation may be effected bystretching plastic sheet until the molecules therein are sufiicientlyoriented. Alternatively, the surface molecules of one or both sides of aplastic sheet may be oriented as by application of linear, frictionalforces thereto without orienting the molecules throughout the remainderof the sheet. In surface orientation, the oriented region adjacent thesurface is of sufiicient thickness to give dichroism when dyed. Thedichroic dye and therefore any image from which the dichroic dye isderived should not penetrate beyond the oriented region at the surfaceand into the unoriented region of the plastic. When the light-sensitivematerial is placed in the carrier by inbibition, the molecules of thecarrier may be oriented either before or after the incorporation of thelight-sensitive material therein.

Plastics which may have their molecules oriented so as to be renderedlight-polarizing when dyed with a dichroic material are herein termedorientable plastics. All other materials are deemed to benon-orientable. As an incident of orientation, any orientable plasticwhen oriented will possess at least one of the following properties. TheX-ray diffraction diagram of the plastic will disclose a fiber structureif the plastic is crystalline and oriented; or mechanically, the tensilestrength is different as measured parallel and transverse to thedirection of orientation if the plastic is oriented, the tensilestrength being greater parallel to the orientation direction; or theplastic will display birefringence if oriented, the birefringence beinggenerally uniaxial around the orientation direction.

Of the carrier materials heretofore set forth, the invention, asintimated, intends to use orientable plastics in the formation of bothlightpolarizing images and nonpolarizing images. At the same time theinvention comprehends the use of hydrophilic materials other thanorientable plastics, gelatin for one example, in the formation ofnonpolarizing images by novel methods which will presently be described.

A support is generally employed for the carrier or carriers of thephotographic films of the inventi-on. The support may be a plasticmaterial, although it may be glass and in certain instances paper, whichmay have a metallic or other reflecting coating provided thereon. Infact any of the films to be later described may be superposed on alight-reflecting backing, at least after image formation, to provide areflection print.

Examples of suitable transparent support materials comprise a cellulosicplastic, for example cellulose esters such as cellulose acetate andcellulose nitrate or cellulose mixed esters such as cellulose acetatebutyrate or cellulose acetate propionate, or a vinyl compound, such asthe vinyl acetate-chloride copolymers, or a suitable condensation typesuperpolymer, such as polyamide or nylon-type plastic. The various typesof cellulose esters such as cellulose nitrate and cellulose acetatebutyrate may be named as preferred transparent materials for thesupport. It is also to be understood that such materials as polyvinylalcohol and regenerated cellulose may be used to provide a support andare to be preferred under practices wherein an exposure control dye isincorporated in a support.

It is desirable in the use of film having several carriers, in each ofwhich one or more images are to be formed, to separate an outermostcarrier and'that next to it by a layer which contains a suitableexposure or light control material or dye. Polyvinyl alcohol andregenerated cellulose provide carrier materials suitable for thispurpose. Alternatively, an exposure control dye may be incorporateddirectly in the carriers as by imbibition. Many dyes which absorb lightand are useful for exposure control are known. Tartrazine, a yellow dye,may be given as one example. Water soluble dyes of this character whichgradually wash out of the photographic element during processing may bereplaced by imbibition prior to the completion of image formation. 0nthe other hand, water insoluble dyes should be removed from thedye-containing layers after image formation by bleaching with an agentwhich will not affect the dye of the formed color image or images.

Instead of using a dye to avoid double exposure, an ultra-violet lightabsorber which is transparent in the visible range of the spectrum, maybe used as a barrier when incorporated in a transparent layer. Organiccompoundsof the class of azines, especially furfuralazine andcinnamalazine, may be employed for this purpose. When an ultra-violetlight absorbing barrier is used between a plurality of layers, selectiveexposure is made with ultra-violet light to which the ferric salts aresensitive.

The different layers of the photographic elements of the drawing may becoated on or laminated to one another. Orientation may be effected afterformation of the element, or in the case of individual layers to belaminated, they may be oriented before or after they are bondedtogether.

With special reference to the flow diagram of Fig. 1, an explanation ofthe manner of forming a .color image in the film illustrated thereinascomprising a support 10 and carrier II, will lead to a furtherunderstanding ofthe invention. Sensitization of the carrier layer H withferric salts may be effected by imbibition of the-film l 0, I l in asuitable sensitizing solution or mixture of solutions. An example ofsolutions-used for this purpose follows immediately.

Solution A r Grams Ferric ammonium citrate in 500 cc. water 175 Ferricammonium oxalate in 500 cc. water 94 Ferric sodium oxalate in 500 cc.water- Water to make 2000 cc.

Generally, solutions A and B are mixed together in equal parts andgenerally are imbibed in the layer which is to be sensitized. Time andtemperature of imbibition follow conventional practice. Alternativelythe potassium ferricyanide mentioned in solution B may be added to theplastic layer during the development of the exposed portion of the film.I

Following sensitization, the carrier layer II is preferentially exposedthrough an appropriate color record by use of a suitable light source(not shown) for example a mercury vapor lamp, carbon arc, photofioodbulb, or strong or direct sunlight. I

Treating the exposed carrier layer ll in water will effectively developthe exposed portions. Exposure of the sensitized layer converts-theferric salts of the formula to ferrous salts in the exposed portionsthereof. I'he ferrous salts 'thus formed in the layer 11 when treatedwith water are changed to a water-insoluble salt in the form of ferricferrocyanide (Prussian blue) to provide a metallic salt image or mordantin the carrier. Unexpo'sed ferric salts are washed out of the film N, Hby the water used for forming the Prussian 'blue image. Toinsure removalof all unexposed-ferric salts, the developing water may be made.slightly. acidic.

While a mixture of photosensitive ferric salts has been :disclosed forsensitizing the films of the invention, it is to be understood that anyof the salts set forth may be used singly for this purpose; It is alsoto be understood that although organic ferric salts of the characterspecified are preferred, inorganic ferric salts may also be employed forthe practice of the invention; For example, successful results may beobtained by sensitizing film with ferric chloride.

Prussian blue forms an excellent mordant for dye bases or dyeintermediates which may be coupled to produce a dye. Coupling procedureoffers a' simple technique for dyeing a selected portion of a carrier.vTo this end; the invention intends to mordant dye bases to Prussianblue mordant images and couple the mordanted dye bases to form desireddyes. In general, any dye base which may be coupled to form a dye may beeinployed. Specifically, diazo dye bases as a class may benamed assuitable for the practice or the invention.

Specific examples of dye bases comprise Naphthinal'Diazo Blue B salt(tetraz'otized and stabilized dianisidine), Diazo Black B salt (p-diazo-'diphenylamine sulphate) and those formed by diazotiz in'g benzidine or4,4-diaminodiph'enylamine or diaminostilbene or diaminostilbenedisulphonic acid. These dye bases when approp'riately coupled providedyes which display substantial di'chrbism and are suitable for use inthe formation of light-polarizing images. Other di'azo dye bases such asdiazotiz'ed aniline and di'azotized naphthionic acid when coupled withan appropriate coupler to give a desired color provide a dye which issubstantially nondichroic. Dye bases of this latter class are includedwithin the scopeof the invention.

The dye basesemployed are in general soluble in ,water and areintroducedinto the layer H by imbibition. A preferred dye base for color work isNaphthinal Diazo Blue 3, and a suitable dye base solution comprises 1.?grms. thereof dissolved in 500 cc. waterto which has been added20g'r'ms. of citric acid.

Imbibition of the layer ll the'dye base solu tion is for about minutesafter which the layer is washed in'a 0.5% aqueous solution of aceticacid for" about 3' minutes-and is then further washed in water for about2 minutes. The function of thisftreatmentin' acetic acid is to wash outexcess dye base without harm to the mordant image: Other acids may beused for this purose. Ihe mordanted dye base may now be converted intoadesired color image by use of an appropriate-coupler.- 1 v The?invention is susceptible to practice with any coupler which will converta dye base to a dye. Specific examples of suitable couplers for use withthe dye bases mentioned may be found insu'bstitution products *ofbenzene and naphthalenecontaining a" hydroxy or amino group, and withthe ortho' or 1 para"- positionsl' free for coupl'iiig. C'oupl'erswhichprovide a magenta image comprise resorcinol, orcinol (methyl resorcinol)naphthionic acid and m-aminophenol; for a cyan image, SS acid(1-amino-8-naphthol- 2,4-disulphonic acid) and S acid (l-amino-S-naphthole l-sulphomc acid); and for yellow image, phenol and m-cresol.For black and white reproduction, diazotized benzidine when coupled with2-amino-8-riaphthol-G-sulphonic acid will give a black dichroic dye. Thecouplers named are water-soluble and are made up into suitable solutionswhich are imbibed in the carrier; Preferred couplers for color workcomprise resorcinol, SS acid and phenol and the time of imbibition forthem is about one minute.

A specific example of a coupling solution for providing a magenta imagecomprises:

Resorcincl v grams 3.5 Sodium hydroxide (10% aqueous solution) =cc 5Water cc An example of a suitable coupling solution for providing a cyanimage comprises:

SSa'cid grams 1.5

Sodium hydroxide (10% aqueous solution) cc 2 Water cc 100 A. suitablecoupling solution for a yellow image comprises:

Phenol grams 3 Sodium hydroxide (10% aqueous solu- V tion') cc 2 Watercc 100 Certain of the dyesformed from the dye bases heretofore describedby coupling with the previously mentioned couplers are soluble whilother of these dyes are insoluble. By a soluble dye, as used in thespecification and claims, there is meant a dye which is solu'ble inwater. For example, when Naphth'inal Diazo Blue B salt is coupled withresorcinol, an. insoluble dye results. On the other hand, whenNaphthinal Diazo Blue B salt is coupled with SS acid, a soluble dye isformed. Still further, Naphthinal Diazo Blue B salt, when coupled withphenol, produces a dye which is difli'cultly soluble.

As noted in the foregoing, all of the dyes. re sulting from the couplingpractices set forth show substantial substantivity to o'rien-tableplastic materials whether these materials are oriented or not.Substantivity as used in the specification and claims means the abilityof a dye to remain substantially fixed in a carrier although subject edto Water and the processing solutions named herein After formation of acolor image component, it is desirable to remove its associated Prussianblue image. This is accomplished by treating the metallic salt with weaksodium hydroxide to convert-the lfrussian blue to ferric hydroxide whichmaybe removed by bathing the photographic elemerit Iii, i l in a dilutesolution of a suitable acid, preferably a weak solution of a strong acidsuch as hydrochloric acid. By making the coupler solution alkaline, asis the case of the coupler solutions mentioned, thePrussian blue will beconverted to ferric hydroxide when the coupling reac-tion is carriedout. On drying, which may or may not be preceded by further washing, thephotographic film ill, I! maybe used or prepared for further color imageformation therein.

Asummary of ,the practices heretofore described is given in the fiowdiagram of Fig. 1 wherein the element Iii, II is shown at differentstages of processing, the first stage in the diagram illustrating theelement after the carrier layer H thereof has been sensitized withferric salts. As indicated by the legend appearing in Fig. 1, thesensitized element is exposed through an appropriate color record and isthen washed in water to form an image in Prussian blue and to remove theunexposed ferric salts from the carrier layer i I. Such procedure causesthe film I0, I I to take on the appearance disclosed in the'second stageof processing illustrated in Fig. 1 wherein the carrier layer ll isshown as containing only an image of Prussian blue.

The next stage of the process which is illustrated in Fig. 1 resultsfrom treatment of the film Ni, ii in accordance with the practicesindicated by legend wherein a dye base, which is mordanted to thePrussian blue image, is reacted with a coupler to form a dye. Removal ofthe Prussian blue mordant leaves the layer l l in the third stage ofprocessing illustrated in Fig. 1 wherein the element It, H contains adye image only which is referred to in the flow diagram by the notationof 1st dye image.

The foregoing has described procedure by which a single color image maybe formed in a carrier. A second dye image representative of anothercolor component of a multicolor image may be formed in the film It, I lin the manner indicated in the legend accompanying Fig. 1, namely, byresensitizing layer l l with ferric salts and repeating the stepspreviously noted. The result of such treatment is shown in the fourthstage of the processing illustrated in Fig. 1 wherein layer H inaddition to the previously mentioned dye image contains an additionaldye image which is indicated by the notation 2d dye image. As intimated,the dye of each color component is of a color suitable for multi-colorimage formation. For convenience, the dye images have been shown asoccupying different portions of the layer M. It will be understood,however, that in normal photographic practice a portion of at least onedye component image of a multicolor image will overlap a portion of atleast one other dye component image of said multicolor image. In thesuccessive formation of color image components, as has been noted, it isnecessary to resensitize the layer between the successive formationthereof. This maybe done by resensitizing the film in the sensitizingsolutions A and B in the manner heretofore set forth.

When dyes of the described character are formed in orientable plasticmaterials, they may be expected to remain substantially fixed thereinwithout diffusion or bleeding during successive color componentformation due to their substantivity to such materials. In the case ofcarriers formed of unorientable materials, for example gelatin, to whichdyes of the character described do not exhibit great substantivity, itis desirable to use dyes which are of an insoluble nature. Analternative practice for multicolor work when carrier materials of thelatter class, such as gelatin, for example, are employed, is to use bothsoluble and insoluble dyes, an insoluble dye being utilized to form thefirst color component. Under such practices a soluble dye could be usedfor the last color component to be formed.

In the case where one or more dye image components are formed in each ofthe carriers of a film having two carriers, for example, on a support,-exposures may be made simultaneously from each side :of the film. Inthis practice it is desirable to employ a light absorbing barrierbetween the two photosensitive layers or to incorporate a suitable dyein the film support to the end of avoiding double exposure of theindividual layers or if desired the last-formed color component couldconsist of Prussian blue itself.

It has been mentioned that a film having two image carriers, such as thefilm of Fig. 2, may be used in three dimensional and also in twodimensional multicolor reproduction. Such a film is desirable in theformation of two dimensional light-polarizing or non-polarizingmulticolor images as it leads to simplification of processing.

For example, carriers 2| and 122 may be sizmultaneously exposed througha different color record for two color components of a multicolor image,following which the film is processed in the manner described to formthe respective color image components in the carriers. If a two colorreproduction is being made, image formation has beencompleted. On theother hand, if a three color reproduction is being made it is onlynecessary to resensitize the film with ferric salts, expose either layerthrough the third color record and process to form the thirdcolor'component in the film.

Thus, in either two color or in three color workone resensitizatilon,one re-exposure of thefilm and subsequent processing are saved ascompared with the case where two or three color image components areformed in asingle carrier.

With certain dyes, such as those mentioned herein, it is desirable totreat each formed color image so as to give it a desired hue. In thecase of the formation of a plurality of color image components, this maybe carried out after all image formation has been completed and the lastmetallic salt image removed. If only one image; of a suit-able color isto be formed, this practice is employed following the removal of themord-ant image for that color image. Treatment is carried out byimmersing the film for from 30 to 60 seconds in a buffer solution ofabout pH 6.8, after which the film is dried and is then ready for use. Asuitable buffer solution for this purpose comprises:

Cic.

Citric acid mol. aqueous solution 25 Sodium phosphate. dibasic(secondary mol. aqueous solution N5 From the foregoing it will beappreciated that the invention is particularly adapted for the formationand processing of photographic films and papers. Films employed by theinvention may be used as transparencies or as reflection prints bymounting them upon a light-reflecting backing such as metalized paper.The photographic elements heretofore disclosed are suited for positiveor negative forming materials flout are especially adapted to positiveprinting purposes from prepared negatives, the latter being equally truelOf photographic papers sensitized with ferric salts.

As hereinbef ore pointed. out, while the invention is described inconnection with photographic films and elements, it is in no way limitedto such usage, but it may be employed with any hydrophilic carrier. Asone example it will be appreciated that designs or images in color or inblack and white may be formed :on various textiles with considerablefacility.

Throughout the specification and claims where the term hydrophilic isemployed, reference is made to a substance or material which shows anafiinity for water or has the ability to absorb or adsorb water.

The term dichroisrn is used herein as meaning'theproperty ofdifi'erential absorption of the components of an incident beam of lightdepending uponthe vibration directions of said components.

Likewise, throughout the specification, the term dichnoic as applied toa material or a dye or a stain means a material or a dye or a stainwhose molecules possess the property of showing dichroism. In thepractice of the invention, this property is displayed when such materialor dye or stain is incorporated in molecularly oriented, hydrophilicplastics of the character described in that the resulting areascontaining the same are light polarizing.

lt has'been pointed out that a light-polarizing or dichroic image has anoptical density which is a function of the direction of vibration of theincident light. This is true of each light-polarizing image produced inall embodiments of the invention. Such images are known as vectographs.

Since certain changes may be made in carrying out the above processeswithout departing from the scope ofthe invention, it is intended thatall matter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

What is claimed is:

1. In a method of forming a dye image in a hydrophilic carriersensitized with ferric salts, the, steps of exposing the carrier,developing the exposed carrier to convert the exposed portion thereof toa Prussian blue image, removing unexposed ferric salts, imbibing intothe carrier a solution of a dye base which will mordant to said Prussianblue, treating the mordanted dye base with acoupler to convert the baseto a predetermined dye a-nd removing the Prussian blue image.

2. In a method of forming a dye image in a hydrophilic carriersensitized with ferric salts, the steps of exposing thecarrier,developing the exposed carrier to convert the exposed portion thereoftoa Prussian blue image, removing unexposed ferric salts, imbibing intothe carrier 2. solution of a dye base which will mordant to saidPrussian blue, treating the mordanted dye base with a coupler to convertthe dye base to predetermineddye which is substantially substantive tothe material forming the carrier, and removing the Prussian blue image.

3., In a method of forming, a dye image in a hydrophiliccarriersensitized with ferric salts, the steps, which comprise exposing thecarrier, developing the exposed carrier to convert the exposedportionthereof to a Prussian blue image, removing unexposed ferric salts,mordanting tothe Prussian blue image a dye base which can be convertedto a soluble dye, treating the mordanted dye base with a coupler toconvert the dye, base to a predetermined soluble dye which issubstantially,substantive to the material formingthe carrier, andremoving the Prussian blue ma-sa 4. In a method of forming a dye imagein a hydrophilic carrier, sensitized with ferric salts, thestepscomprising, exposing the carrier, developing the exposed carrier totransform the exposed portion thereof to a Prussian blue image, removingunexposedferric salts, mordanting to the Prussian blue image a dye basewhich can be converted to a substantially insoluble dye, treating themordanted dye base with a coupler to convert the dye base to apredetermined insoluble dye, and removing the Prussian blue image.

5. In a method of forming a dye image ina hydrophilic carriersensitized, with ferric salts, the stepsv of exposing the carrier toprovide at least one ferrous salt image therein, developing eachferroussalt image to convert it to Prussian blue, removing unexposedferric; salts from the carrier, imbibing into the carrier 2. solution ofa diazo dye base which will mordant to said Prussian blue, treatingthemordanted dye base with a, coupler to convert the dye base topredetermined dye, and removing the Prussian blue mordant.

6. In a method of forming a dye image in a hydrophilic carriersensitized with ferric salts, the steps of exposing the carrier toprovide at least, one ferrous salt image therein, developing eachferrous salt image to convert it to Prussian blue, removing unexposedferric salts from the carrier, mordanting Naphthinal Diazo Blue 13 saltto saidPrussian blue, treating said mordanted Naphthinal Diazo Blue Bsalt with a coupler to form a, predetermined dye, and removing thePrussian blu mordant.

7. In a methodof forming a light-polarizing image in a carriercomprising a hydrophilic, molecularly oriented, linear polymeric plasticwhich is sensitized with ferric salts, the steps of predeterminedlyexposing the carrier to light, converting the exposed-ferric salts toPrussian blue to provide an image in terms of Prussian blue in thecarrier, removing unexposed ferric salts, imbibing into the carrier asolution of a dye base which will mordant to said Prussian blue andwhich may be converted to a predetermined dichroic dye which is. solubleand substantially substantive to thematerial of saidcarrier, treatingthe mordanted dye base with a coupler to convert the dye base to saidpredetermined dichroic dye, and removing the Prussian blue image.

8. In a method of forming a light-polarizing image in a carriercomprising a hydrophilic, molecularly oriented,linear polymeric plasticwhich is sensitized with ferric salts, the stepsoi exposing the carrierto light, converting the exposed ferric salts to Prussian blue toprovide an image in terms of Prussian blue in the carrier, removingunexposed ferric salts, imbibing into the carrier 2. solution of a dyebase which will mordant tosaid Prussian blue and which may be convertedto a predetermined dichroic dye which is substantially insoluble andsubstantially substantive to the material of the carrier, treating themordanted dye base with a coupler to convert the dye base to saidpredetermined dichroic dye, and removing-the Prussian blue image.

9. In a method of forming a dye image in a carrier comprising gelatinwhich is rendered light sensitive with ferric salts contained therein,the steps of exposing the carrier to light, converting the exposedferric salts to Prussian blue to provide an image in terms of Prussianblue in the carrier, removing unexposed ferric salts, mordanting to saidPrussian blue image a dye base which can be converted to a soluble dyeto provide a dye image in th carrier, reacting the mordanted dye basewith a coupler to form a predetermined dye which is soluble, andremoving the Prussian blue mordant,

10. In a method of forming a dye image in a hydrophilic, linearpolymeric plastic which possesses the property of being orientable andwhich is sensitized with ferric salts, the steps of exposing thecarrier, developing the exposed carrier to convert the exposed portionthereof to aPrussian blue image, removing unexposedferric salts,imbibing into the carrier a solution of a dye base which will mordant tosaid Prussian blue, treating the mordanted dye base with a coupler toconvert the base to a predetermined dye, and removing the Prussian blueimage.

11. In a method of forming a dye image in a carrier formed ofhydrophilic material, the steps of sensitizing the carrier with ferricsalts, exposing the carrier to light to form at least one ferrous saltimage therein, converting each ferrous salt image to Prussian blue,removing unexposed ferric salts from the carrier, mordanting a dye baseto the Prussian blue, reacting the mordanted dye base with a couplerhaving the ability to convert the dye base to a predetermined dye, andremoving the Prussian blue mordant.

12. In a method of forming a light-polarizing image in a hydrophilic,molecularly oriented, linear polymeric plastic carrier, the stepscomprising sensitizing the carrier with ferric salts, exposing thesensitized carrier to light to provide an image in the exposed portionthereof, developing the exposed portions of the carrier to convert themto Prussian blue, removing unexposed ferric salts from the carrier,mordanting a dye base to the Prussian blue, treating the mordanted dyebase with a coupler to convert the dye base to a predetermined dichroicdye which will remain substantially substantive to the plastic carrier,and removing the Prussian blue mordant.

13. In a process of color photography in which a series of colorcomponent images is formed in sequence in a hydrophilic carrier, thesteps leading to the formation of any image of said series whichcomprise introducing light-sensitive ferric salts into the carrierwhereby to render it light sensitive, preferentially exposing thecarrier, developing the exposed carrier to convert the exposed portionthereof to a Prussian blue image, removing unexposed ferric saltswhereby the carrier is substantially insensitive to light, mordanting adye base to said Prussian blue image, treating the dye base with acoupler to convert the dye base to a predetermined dye, and removing thePrussian blue image.

14. In a process of color photography in which a series of colorcomponent images is formed in sequence in a hydrophilic carrier, thesteps leading to the formation of any image in said series whichcomprise imbibing a solution of light-sensitive ferric salts into thecarrier whereby to render it sensitive to light, preferentially exposingthe carrier to light, developing the exposed carrier to convert theexposed portion thereof to a Prussian blue image, substantially freeingthe carrier of unexposed ferric salts whereby the carrier is renderedsubstantially insensitive to light, imbibing into the carrier a solutionof a dye base which will mordant to said Prussian blue, treating themordanted dye base with a coupler to convert the dye base to apredetermined dye which is substantially substantive to the materialforming the carrier, and removing the Prussian blue image.

15. In a process of producing a multicolor, light-polarizing image bythe formation in sequence of a plurality of dye images in a hydrophilic,molecularly oriented, linear polymeric plastic, each dye imagerepresenting an individual color component and comprising a dichroic dyeof a predetermined color, the steps leading to the formation of anycomponent image in said plurality which comprise sensitizing theoriented carrier by imbibition with light-sensitive ferric salts,preferentially exposing the carrier to light, developing the exposedportion of said carrier to an image comprising Prussian blue,substantially freeing the carrier of unexposed ferric salts whereby thecarrier is rendered substantially insensitive to light, mordanting tosaid Prussian blue image a dye base which may be coupled to a dichroicdye of a predetermined color, coupling the dye base to a dichroic dye bythe treatment of the dye base with a coupler which will react with thedye base to form said predetermined dichroic dye, and removing thePrussian blue image whereby the carrier is in a condition wherein it issubstantially insensitive to light and contains at least onelight-polarizing dye image.

HELEN P. HUSEK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,197,994 Butement Apr. 23, 19402,252,718 Mannes et al. Aug. 19, 1941 2,289,714 Land July 14, 19422,333,359 Bunting Nov. 2, 1943.

